- An open joint between frame and brickwork lets in rain and draughts
- Insulation that stops short of the frame creates a cold edge and a risk of condensation
- A missing airtight finish inside, letting moisture into the construction
- A frame set at the wrong depth in the wall, so the junctions no longer line up
Building detail · Window frame
Window frame in a cavity wall: seals and cavity tray
The junction between window frame and cavity wall decides whether a facade stays dry, draught-free and well insulated. Here you can see how such a junction is built up, where it often goes wrong and what we look out for in the drawing.
- Watertight outside, airtight inside
- Insulation running unbroken up to the frame
- A detail that suits the existing facade
Principle sketch
Build-up of the detail
Horizontal section at the side of a window frame in a cavity wall. The numbers in the sketch refer to these parts:
- Outer leaf (brickwork)
- Air cavity
- Cavity insulation
- Inner leaf (calcium silicate)
- Timber frame jamb
- Sealing tape between frame and brickwork
- Airtight seal on the inside
- Insulating glass
Common mistakes
Where it often goes wrong
Leaks, condensation and cracks usually start at the junctions, not in the middle of a wall or roof.
In the drawing
What we look out for
We work out the detail for your home, based on a site survey and the chosen materials.
- The position of the frame within the depth of the wall
- Water barriers and drainage below and above the frame
- The order: watertight and vapour-open outside, airtight and vapour-retarding inside
- An outer-leaf rebate that covers the frame
- The connection to the window sill, interior finish and ventilation
In a renovation the existing cavity is not always insulated or of even width. We then match the detail to what is actually there, after a site survey.
Do new window frames need a permit? Read more about window frame drawings at Aboss Bouwadvies (in Dutch).
Detail FAQ
Frequently asked questions about this detail
Should a window frame sit in the cavity or against the inner leaf?
Both are common. The choice depends on the cavity width, the insulation, the frame type and the existing facade. What matters is that the water barrier, insulation and airtight layer connect without gaps.
What is sealing tape?
A self-expanding tape that seals the joint between frame and brickwork against rain and wind, while still letting the frame move.
Why must the inside be airtight?
Warm, humid indoor air escaping through a joint can condense inside the construction. An airtight finish on the inside prevents this.
Can I use this principle sketch for my own home?
The principle sketch shows the build-up, but it is not a working drawing. Dimensions, materials and fixings depend on your home. We work out the detail for your situation.
Detail library